Pharmaceutical compositions usually require a suitable solvent or carrier system to disperse the active agent to enable the composition to be administered to a patient. The solvent must typically be capable of solubilizing or dispersing a therapeutically effective amount of the active agent to produce an effective injection composition. Moreover, the solvent system must be compatible with the active agent and be non-toxic to the patient.
Numerous pharmaceutical agents are not sufficiently soluble in any one solvent to enable the resulting composition to be effective. To overcome the disadvantages of the limitations of the solvent to solubilize the active agent, mixtures of two or more solvents are sometimes used. These co-solvent systems are suitable for solubilizing many pharmaceutical agents which cannot otherwise be solubilized or dispersed in a carrier system.
One example of a co-solvent system incorporates a mixture of a polar solvent and a non-ionic solvent, such as a mixture of a polyethylene glycol and Cremophor EL. Cremophor EL is a condensation product of castor oil and ethylene oxide sold by BASF. Another suitable co-solvent system for many pharmaceutical agents is a 50:50 mixture of ethanol and Cremophor EL. Although these co-solvent systems can be effective in solubilizing many compounds, they are not without their disadvantages. For example, co-solvents of ethanol and Cremophor are known to result in particulates forming upon dilution with infusion solutions. In addition, fibrous precipitates of unknown composition form in some compositions during storage for extended periods of time. It is generally believed that the precipitates are decomposition byproducts of either components in the solvent or the solubilized agent.
In WO91/02531, published Mar. 7, 1991, Cremophor is disclosed as reversing the multi-drug resistance phenotype of a tumor cell without altering the drug sensitivity of the parent cell line. Cremophor is also disclosed to increase hemopoiesis reconstituting capacity and/or maintain hemopoiesis reconstituting capacity following perturbation of bone marrow to protect a patient during radiation and/or chemotherapy cancer treatments.
Another example of a pharmaceutical composition including a co-solvent system is Taxol which contains paclitaxel in a 50:50 mixture of ethanol and Cremophor EL. Paclitaxel is isolated from the Pacific yew bark and has been used to treat cancer patients. Although the ethanol and Cremophor EL co-solvent system is effective in solubilizing sufficient amounts of the paclitaxel, the resulting composition has been shown to have a limited shelf life. During storage for extended periods of time, the potency or pharmaceutical activity of the composition can decrease as much as 60%.
It has been discovered that commercial grade Cremophor EL with ethanol as a co-solvent, although effective in solubilizing pharmaceutical agents, produces injection compositions that exhibit instability over extended periods of time. In particular, pharmaceutical compositions of Taxol in a co-solvent of 50:50 by volume of dehydrated ethyl alcohol and commercial grade Cremophor EL exhibit a loss of potency of greater than 60% after storage for 12 weeks at 50.degree. C. The loss of potency is attributed to the decomposition of paclitaxel during storage.
Previous efforts to develop a shelf stable composition of some pharmaceutical compositions in various co-solvent systems have not been entirely successful. Thus, there is a continuing need in the art for a co-solvent system capable of being used for preparing stabilized compositions and, in particular, stabilized injection compositions containing a pharmaceutical agent.